1. Field of the Invention
The present invention relates to a hollow package, particularly a hollow package in which a package body having a recess is sealed with a transparent sealing plate, and also relates to a method for fabricating the same.
2. Description of the Related Art
A solid-state image apparatus of a typical leadless chip carrier (LCC) generally has a structure, as shown in FIG. 4, in which a ceramic package body having a recess with a step receives a solid-state image device, and the package body is sealed with a glass plate. In the drawing, symbol a represents a first layer of the ceramic package, which is flat, and a metallized lead d is formed thereon, extending from the side to the outer bottom. Symbol b represents a second layer of the ceramic package, which is in the shape of a rectangular frame, and a metallized lead d is formed thereon, extending from the upper surface to the side, and also connecting to the lead d on the first layer a. Symbol c represents a third layer of the ceramic package, which is in the shape of a rectangular frame, and an opening of the third layer c is larger than an opening of the second layer b. The two openings form a recess e, for receiving a solid-state image device, having a step with the first layer a serving as the inner bottom.
Symbol f represents a solid-state image device received in recess e on the ceramic package, symbol g represents bonding wires connecting between electrodes of the solid-state image device e and the metallized leads g and symbol h represents a transparent sealing plate composed of glass bonded onto the upper surface of the package with an adhesive i therebetween for sealing the recess e.
Next, a method for fabricating the package will be described. Unsintered package sheets a, b, and c (corresponding to the first layer a, second layer b, and third layer c), which are so-called xe2x80x9cgreen sheetsxe2x80x9d or xe2x80x9cgreen ceramic sheetsxe2x80x9d, are prepared. The green lead d is formed on the individual sheets a and b. The individual sheets, a, b and c are deposited at predetermined positions and are sintered, whereby the package is obtained. Next, the metallized lead d is formed by plating, and die bonding is performed to the solid-state image device f, followed by wire bonding. Lastly the transparent sealing plate h composed of glass is bonded onto the upper surface of the package body. Thus, a solid-state image apparatus is complete, in which the solid-state image device is received in the ceramic hollow package.
Because of the high cost of materials and processing for ceramic hollow packages, it has been difficult to reduce the fabrication costs of solid-state image apparatuses. Therefore, the present inventor and others have made attempts to fabricate hollow packages from a resin instead of ceramic by applying the molded interconnect device (MID) technique widely used in various electronic devices to hollow packages. This is because an MID is an electronic component in which a circuit (three-dimensional circuit) is formed on a three-dimensional part produced by injection molding, and a resin material which is considerably less expensive in comparison with a ceramic material is used, and also the inexpensive injection molding technique which is easier and faster than sintering is used for formation. In particular, it is greatly advantageous that injection molding be performed once to enable the formation of a package body even in the case of a three-dimensional part, which is in contrast to the complex fabrication of a ceramic hollow package requiring the steps of forming three-layers of green sheets, depositing them at correct positions, and sintering.
The current MID technique, however, has been found to be unsuitable for hollow packages which receive semiconductor devices such as solid-state image devices. The reason is that the general MID, a thermoplastic resin having a high thermal coefficient of linear expansion, for example, a liquid crystal polymer (LCP) or PPS, is used, and there is a large difference in thermal coefficient of linear expansion between the thermoplastic resin and glass used as the transparent sealing plate. Therefore, if the hollow package is sealed with the transparent sealing plate, either the sealing plate or the resin forming the package body will be easily cracked, resulting in difficulty in maintaining air-tightness.
Also, since leads, i.e., lands, and areas between leads, i.e., spaces, intervene between the transparent sealing plate and the package body which are to be bonded together, if the general adhesion technique using a thermosetting resin is employed, an internal pressure between the package body and the transparent sealing plate increases because of the heating for adhesion, resulting in air leakage through the spaces of the lands-and-spaces. This also does not allow air-tightness to be maintained.
In the case of a ceramic hollow package, since a plurality of sheets having a lead on the surface are deposited, a lead for connecting between the interior of the hollow package and the exterior can be formed even without placing wires on the upper surface of the hollow package. On the other hand, in the case of a package body formed by using the MID technique, unless a through-hole is formed on the package body, and the interior of the package body and the external lead are connected via the through-hole, the lead must be formed on the surface of the package body, and thus, the lead inevitably runs on the upper surface of the package body which is the connecting section between the package body and the transparent sealing plate. As a result, the lands-and-spaces are formed on the upper surface of the package. The thickness of the spaces is substantially equal to the thickness of the lead, for example, 20 to 30 xcexcm. Generally, since a thermosetting resin is used as the adhesive, if the conventional technique is followed, heat treatment must be performed to generate adhesive bonding in the adhesive material. If heat treatment is performed, the internal pressure within the hollow package increases inevitably and even if a resin for adhesion is buried in the spaces, air leakage occurs, and thus, it is impossible or extremely difficult to maintain air-tightness.
As described above, it seemed impossible to apply the MID technique to a hollow package, in which a semiconductor device such as a solid-state image device placed in a package body is sealed with a transparent sealing plate, for example, glass. However, the present inventor continued to investigate in order to overcome the difficulty, and finally achieved the present invention.
It is an object of this invention to provide a method for fabricating a hollow package with a resin, in which an electronic component, for example, a semiconductor device, placed in a recess on a package body is sealed with a transparent sealing plate, such that the cost of materials and processing is reduced and the price of an electronic apparatus (for example, a solid-state image apparatus) provided with the hollow package is reduced.
In accordance with one aspect of the present invention, a hollow package includes a package body having an MID structure composed of an epoxy resin having a low thermal coefficient of linear expansion and a transparent sealing plate which is bonded onto the upper surface of the package body with an ultraviolet-curable resin. The package body includes leads, for extracting electrodes of a contained electronic component, which extend from the inner surface of a recess, via the upper surface of the package body, to the peripheral surface. The transparent sealing plate protects the recess on the package body from the exterior.
In accordance with the hollow package of the present invention, firstly, since the epoxy resin having a low thermal coefficient of linear expansion is used as a material to form the package body, the difference in thermal coefficient of linear expansion between the transparent sealing plate and the package body can be minimized, and even if the interior of the hollow package is sealed with the transparent sealing plate, the transparent sealing plate or the resin forming the package body is not easily cracked by thermal stress, enabling air-tightness to be maintained.
Secondly, since the ultraviolet-curable resin is used as the adhesive for bonding the package body and the transparent sealing plate together, no heating is required in order to generate adhesive bonding. Accordingly, it is possible to maintain air-tightness since there is no heating which may increase the internal pressure between the package body and the transparent sealing plate and thus may cause air leakage through the spaces in the lands-and-spaces described above.
Thirdly, since the package body is composed of a resin which is less expensive in comparison with ceramic, the cost of materials can be reduced, and also since the package body is formed by infection molding which does not require the deposition of green sheets or sintering, the cost of formation can also be reduced. Accordingly, the price of an electronic apparatus provided with the hollow package can be reduced.
In accordance with another aspect of the present invention, a method for fabricating a hollow package includes the steps of forming a package body by three-dimensional injection molding of an epoxy resin having a low thermal coefficient of linear expansion; roughening a surface of the package body; forming a wiring layer by electroless plating; forming leads by patterning the wiring layer; receiving an electronic component into a recess of the package body and connecting electrodes of the electronic component to the leads; and then bonding a transparent sealing plate onto an upper surface of the package body with an ultraviolet-curable resin.
In accordance with the method for fabricating the hollow package, since the package body is composed of a resin which is less expensive in comparison with ceramic, the cost of materials can be reduced, and also since the package body is formed by injection molding which does not require the deposition of green sheets or sintering, the cost of formation can also be reduced. Accordingly, the price of an electronic apparatus provided with the hollow package can be reduced.
Since the surface of the package body is roughened after the formation, adhesiveness of the wiring layer subsequently formed can be increased, and the bond strength of the transparent sealing plate to be bonded to the hollow package can be increased. Also, because of the roughening, connectivity between the leads and, connectors, for example, connecting wires, can be strengthened.
In accordance with still another aspect of the present invention, a solid-state image apparatus includes a package body composed of an epoxy resin having a low thermal coefficient of linear expansion and a transparent plate bonded onto the upper surface of the package body. The package body includes a recess for receiving a solid-state image device, and leads, which are connected to electrodes of the solid-state image device, extending from the inner surface of the recess, via the upper surface of the package body, to the peripheral surface.